1. Field of the Invention
The present invention relates to an apparatus for reproducing encoded data, and particularly, to a technique of speedily and accurately identifying a position to seek in encoded data and reducing an error from a desired time point from which the encoded data must be reproduced.
2. Description of Related Art
There are a variety of methods to encode data. To reproduce original data from encoded data, a reproducing apparatus employs an encoded data analyzer and a decoder. In the reproducing apparatus, a function of finding a required time point or position in encoded data and decode the data from the found time point or position is called a seek function. When a target time to seek in encoded data is specified, the reproducing apparatus computes a data size corresponding to the target time, skips the encoded data for the computed data size, reads the encoded data from a proper position around an end of the skipped data, and reproduces the read part of the encoded data.
Encoded data contained in an ASF file or an MP4 file has information concerning a relationship between time and position, and therefore, it is easy to correctly identify a time or position to seek in the encoded data. Any encoded data having no information about a time-position relationship also allows to determine a target time to seek in the encoded data if it keeps information about a bit rate. The bit rate information and the target time are sufficient to correctly compute a data size corresponding to the target time and identify the time to seek in the encoded data.
As the first related art, Japanese Laid-open Patent Publication No. 2000-182326 (in particular, FIG. 1 thereof) discloses a simultaneous recording/reproducing apparatus and a simultaneous multi-channel reproducing apparatus. This related art discloses a system controller 108 and a buffer memory 102. Detecting that an amount of data accumulated in the buffer memory 102 reaches a predetermined value, the system controller 108 suspends to read data from an optical disk 109 and continuously records the data in the buffer memory 102 to the optical disk 109. This related art also discloses a system controller 1408 that manages a zone of an optical disk 109 to which data is recorded and controls a motor 1412 to a rotation speed appropriate for the zone. This rotation speed is maintained for a reproducing operation.
As the second related art, Japanese Laid-open Patent Publication No. 2005-20339 (in particular, FIG. 1 thereof) discloses a technique of realizing a seek operation on multiplex data that has no frame information.
For the first related art, it is difficult to correctly determine a position to seek in encoded data if the encoded data contains no information about bit rate or relationship between time and position. To correctly determine a target position to seek in such encoded data, there is an idea to decode all frames and measure a reproducing time up to the target position. This idea involves an enormous amount of calculations, and therefore, is inapplicable to a system having limits on processing cost, performance, and computation resources.
On the other hand, the second related art involves a problem of long processing time because it computes an average time from a total data size and total reproduction time of given multiplex data.